1. Field of the Invention
The invention covered by the present patent application relates to a method for the production of an electron source substrate provided with an electron emitting element and a method for the production of an electronic device using the substrate.
2. Related Background Art
The electron emitting element has been heretofore known in two broadly divided types, i.e. the thermoelectron emitting element and the cold cathode electron emitting element. The cold cathode electron emitting element comes in such types as the field emission type (hereinafter referred to as “FE type”), metal/insulating layer/metal type (hereinafter referred to as “MIM type”), and surface conduction type, for example.
As examples of the FE type electron emitting element, those elements which are disclosed in W. P. Dyke & W. W. Doran, “Field Emission,” Advance in Electron Physics, 8, 89 (1956) or C. A. Spindt, “Physical Properties of Thin-film Field Emission Cathodes with Molybdenium Cones,” J. Appl. Phys., 47, 5248 (1976) have been known.
As an example of the MIM type electron emitting element, the element which is disclosed in C. A. Mead, “Operation of Tunnel-Emission Devices,” J. Appl. Phys., 32, 646 (1961) has been known.
As an example of the surface conduction type electron emitting element, the element which is disclosed in M. I. Elinson, Radio Eng. Electron Phys., 10, 1290 (1965) has been known.
The surface conduction type electron emitting element utilizes a phenomenon that flow of an electric current parallel to the surface of a thin film of small area formed on a substrate results in emission of electrons. The surface conduction type electron emitting elements include the element using a thin film of Au reported in G. Dittmer: Thin Solid Films, 9, 317 (1972), the element using a thin film of In2O3/SnO2 reported in M. Hartwell and C. G. Fonstad: IEEE Trans. ED Conf., 519 (1975), and the element using a thin film of carbon reported in Hisashi Araki et al.: Vacuum, Vol. 26, No. 1, page 22 (1983) in addition to the element using a thin film of SnO2 proposed by Elinson as mentioned above.
As a typical example of the surface conduction type electron emitting element, the construction of the element proposed by M. Hartwell et al. as mentioned above is illustrated in the form of a model in FIG. 20. In the figure, 1 denotes a substrate and 4 an electroconductive thin film which is formed of a metal oxide in the pattern shaped like the letter H by sputtering and so forth and made to incorporate therein an electron emitting portion 5 by a treatment of electrification called an energization forming which will be specifically described herein below. As illustrated in the figure, the interval L between element electrodes 2 and 3 is set at a length in the range of 0.5 to 1 mm and the width W′ of the thin film at 0.1 mm. The electron emitting portion 5 is illustrated by way of model because the position and shape thereof are unclear or indefinite.
In the surface conduction type electron emitting element of this class, the practice of subjecting the electroconductive thin film 4 to the treatment of electrification called energization forming in advance of the emission of electrons thereby forming the electron emitting part 5 thereof has been in vogue. To be specific, the energization forming is aimed at causing an electron emitting portion to form by means of electrification. It consists, for example, in applying a DC voltage or very gradual elevation of voltage to the opposite terminals of the electroconductive thin film 4 mentioned above thereby forcing this thin film to sustain local fracture, deformation, or degeneration and, as a result, allowing formation of the electron emitting portion 5 in an electrically highly resistant state. The treatment, for example, locally inflicts a fisure to the electroconductive thin film 4 to enable this thin film to emit electrons from the neighborhood of the fisure. The surface conduction type electron emitting element which has undergone the energization forming treatment mentioned above is such that it is enabled to effect emission of electrons from the electron emitting part 6 in response to the application of voltage to the electroconductive thin film 4 and the consequent induction of flow of an electric current through the element.
The surface conduction type electron emitting element of the quality described above enjoys simplicity of construction and allows for the manufacture thereof by the use of the conventional technique of semiconductor production and, therefore, brings about the advantage of enabling a multiplicity of surface conduction type electron emitting elements to be formed as arrayed over a large surface area. Various applied studies in the application of this characteristic feature have been conducted. Charged beam sources and image forming devices such as display apparatuses may be cited as apt examples of the targets of the applied studies.
The construction of the electron emitting element disclosed by the present applicant for patent in JP-A-02-56822 is illustrated in FIG. 19. In this diagram, 1 denotes a substrate, 2 and 3 each an element electrode, 4 an electroconductive thin film, and 5 an electron emitting portion. Various methods are available for the production of the electron emitting element. For example, the electron electrodes 2 and 3 are formed on the substrate 1 by the vacuum thin-film technique popular in semiconductor processes and the photolithographic etching technique. Then, the electroconductive thin film 4 is formed by a dispersion coating method such as, for example, the spin coat. Thereafter, the electron emitting part 5 is formed by applying voltage to the element electrodes 2 and 3 thereby effecting a energization treatment. The conventional method of production cited above, when used to form a multiplicity of elements arrayed on a large surface area, has the disadvantage of rendering indispensable the provision of a photolithographic etching device of large scale, necessitating a large number of steps, and exalting the cost of production. As a means for overcoming these defects by patterning the electroconductive thin film of the surface conduction type electron emitting element without using the semiconductor process, a method for directly depositing a solution containing a metallic element in the form of liquids on a surface by the principle of ink jet has been proposed (as in JP-A-08-171850).
The conventional ink jet methods which are disclosed in JP-A-08-171850 and so forth, however, effect the direct deposition of liquids by the use of such a single head as is illustrated in FIGS. 18A, 18B, and 18C (the component parts illustrated therein have the same meanings as those of FIG. 19). As the substrate gets larger in surface area, a lot of time is required for patterning one substrate, and there is a limit on the increase in the throughput. The conventional methods also have the disadvantage of boosting the cost of equipment because it requires the stroke of the relative motion between the substrate and the head to be increased in accordance with the size of the substrate.
The task assigned to the present invention consists in decreasing the time required for the production of the electron source substrate, increasing the yield of the production of electron source substrates, and improving the electron source substrate in quality.